In the prior art, headless pivot rods have been retained in place in pivot sites of modular link belts by various structures either integral with the modular belt links or affixed thereto. However prior art structures have introduced operational problems and have not proved reliable under some conditions encountered in the normal expected conditions encountered in belt operation. For example movable end caps that may be bent out of the way are subject to fracture or vibration under certain belt operating conditions. Non-integral link attachments may become dislodged to permit rods to exit the belt edges and/or may cause catastrophic belt failures. Furthermore they require manufacturing and stocking of additional belt parts beyond belt links and rods.
It is to be realized that articulation of the belt around sprockets and other operating conditions can lead to vibration and chatter of a rhythmic nature and regionally distributed stresses and forces in end-to-end connected modular links under load that induce pivot rods to move axially out of their pivot sites to extend through the belt edge causing belt failure. Furthermore, smaller diameter and more flexible plastic pivot rods are subject to wear and strain under loading and tension conditions that reduces optimum performance over time and are subject to replacement from time to time as a matter of failure or preventive maintenance. Thus, inconsistent requirements of expediting pivot rod replacement and reliably occluding the rods into their pivot sites are placed upon pivot rod retention structure.
Any pivot rod retention system that requires flexibility of the pivot rods not only precludes the use of metallic rods such as steel, but also may compromise desired long wear and heavy belt load capacity by required use of excessively flexible rods.
Thus, it is an objective of this invention to provide an improved pivot rod retention system that resolves these prior art deficiencies.
A more particular objective of this invention is to provide a pivot rod retention system integrally formed as a resident stationary part of the modular plastic links from which modular conveyor belt systems are constructed.
U.S. Pat. No. 5,332,084, C. G. Greve, Jul. 26, 1994 to some extent resolves the foregoing prior art problems and provides a resident stationary part of the link as an entry guide for flexible plastic rod that must bend for insertion at a belt edge entry position. However, under certain belt operating conditions, for example, where vibration of the unsupported ends of the pivot rod may be induced, the rod may escape the rather small area crescent shaped occlusion member retaining the rod from leaving the edge of the belt.
In U.S. Pat. No. 4,972,942, W. G. Faulkner, Nov. 27, 1990, an edge guard is attached to one side of a link from which a pivot rod extends to prevent interference and to occlude the pivot rod preventing it from passing through the edge guard. To enter or remove a pivot rod from the belt edge it is required to provide elongated pivot rod apertures in all the interdigitated link ends to provide a significant amount of movement of two end-to-end modules toward each other. Thus, the pivot rods may not be removed or introduced from the edge of a belt in normal conveyance position in the field without introducing slack such as by removing the belt from its drive sprockets. Furthermore with the longitudinal shaped apertures in both link ends the pivot rod can introduce impact stresses and have excessive lateral mobility including skewing to positions non-normal to the belt edge under certain operating conditions.
Accordingly it is an object of this invention to provide improved pivot rod occlusion structure at the edge of the belt that facilitates changing of pivot rods and which reliably occludes the pivot rod and retains it in a pivot site in a normally disposed position from the belt edge.
Further it is an object of this invention to provide a greater range of reliability in retention of headless pivot rods by resident stationary occlusion structure integrally formed in the link which permits a wide range of pivot rods from flexible plastic to stiffened steel construction to be readily entered or removed from an edge of an unloaded belt disposed in operational condition in the field.